Vertical grinding mills are widely used in industrial process applications in the reduction and/or pulverization of ore, rock, minerals and other input materials for subsequent processing in mining applications, as well as for example, in the manufacture of fertilizers, cement, glass and ceramics. Conventionally, vertical grinding mills are provided with a grinding tank which is adapted to receive both a volume of solution and the material to be ground or pulverized as either part of a batch or continuous process. An impeller assembly is provided with a mixing or grinding blade which is positioned in a lower region of the grinding tank. When rotated, the mixing blade effects the mixing and physical abrasion of the solution and input material to form a slurry in which fine reduced particles of the infed material is contained in suspension, and which then flows or is pumped from the grinding tank for further processing.
To better effect pulverization, it is furthermore known to introduce into the bottom of the grinding tank, a quantity of hardened metal balls. When introduced, the cascading movement of such balls, combined with the rotary agitation of the mixing blade, achieves more effective and uniform material pulverization and grinding.
The applicant has appreciated that conventional vertical grinding mills, and in particular ball mills, continue to suffer the disadvantage that the input material may reside within lower regions of the grinding tank for insufficient time to achieve the desired materials size reduction/pulverization. In particular, where slurries are formed having higher input materials to grinding solution ratios, coarser ground materials of a pebble size or greater may tend to flow with the slurry outwardly from the grinding tank prematurely. The inclusion of coarser materials in the output slurry has the potential to adversely affect subsequent manufacturing steps. This may be of greatest importance where the relative amount of ground material to solution is more critical for the production of final products, as for example, where vertical mills are used as part of a lime slaking process in the production of slaked lime for pollution control applications.